This invention is concerned with magnetic detection apparatus, particularly of the type employing fluxgate sensors for locating magnetic objects.
A magnetic locator presently marketed by the assignee of the present invention is disclosed, for example, in U.S. Pat. Nos. 3,894,283; 3,909,704; 3,961,245; 4,110,689; and 4,163,877 and has been highly successful. As is evident from the foregoing patents, the locator and its method of manufacture are superior in several significant respects compared to the prior art. The present invention provides further significant improvements, as will become apparent hereinafter. The following brief description of the magnetic locator presently marketed will provide a background for those improvements.
The housing of the locator presently marketed is assembled from several separate components including an aluminum tube, an aluminum plate that is attached to one end of the tube, and an aluminum cover that is attached to the plate to form a casing. The user holds the locator by grasping the tube or the casing. A sensor assembly is formed by mounting a pair of magnetic sensors in oppositely directed notches at the ends of an aluminum sensor-support tube. One sensor is pre-assembled with a stiff excitation wire that is passed through the tube and is then assembled with the other sensor. Signal leads from the sensors extend along the exterior of the sensor-support tube. Thick foam pads are taped to the exterior of the sensor-support tube, and then the sensor assembly is inserted in the tube of the housing. The excitation wire is then soldered to a printed circuit board mounted on a chassis of an electrical unit that is mounted on the plate of the housing. By virtue of the excitation wire and the foam pads, the position of the sensor assembly relative to the electrical unit is established, but to prevent the possibility of any relative movement that is likely to produce a measurement error, a U-shaped bail has its ends bent into notches in the sensor-support tube and its bight attached to the chassis by a screw. An ON/OFF sensitivity control is also mounted on the plate of the housing and is connected to the printed circuit board by flexible leads.